I've seen it suggested on TRP that men only have interest in women for sex and they only endure relationships so they can get sex. Based on the people I know, almost every guy I know has sought out being in a relationship over casual sex. That includes everyone from virgins I know to guys who can and do get laid trivially. It seems to me they want the emotional support and companionship more than they want the sex. That said, I should note that almost everyone I know is college graduated, middle class, and white or asian so we're talking about a very specific demographic.